[Paraview] Questions regarding: volume calculation, xyplot along a curve and tensor calculation

[Jie Xu]

Hi Berk,

Thanks for looking at my questions.

1) I attached a sample data set: test.vtk, and the screenshot of my
paraview window, from which you can see that the clip is created at
(0,0,0) with radius of 50e-6, and the calculated volume is
3.32862e-13, which is much less than what it should be.
(Interestingly, in this specific case, the calculated volume is about
2/pi times the real volume.)

2) Thanks for letting me know.

3) Unfortunately, I have no experience with Python. Now I am trying to
see if I can use matlab to do the tensor calculates and modify the vtk
file readable by paraview.

Regards,
Jie

On Thu, Apr 9, 2009 at 1:51 PM, Berk Geveci <berk.geveci at kitware.com> wrote:
> Hi Jie,
>
>> 1) Volume calculation:
>> I found that the "integrate variables" over a sphere clip never gives
>> the correct volume. For example, I tried to use a very simple geometry
>> and a very fine mesh (a 200x200x200 micron cube with 2 micron cube
>> elements), and use paraview to generate a sphere clip that has radius
>> of 50 micron in the center of that cube, then I apply the "integrate
>> variables" filter to the clip and show the "Cell Data", it gives a
>> volume of 4.78818e-13 instead of 5.236e-13, which is 4/3*pi*r^3. The
>> discrepancy is so large that it just cannot be due to the coarseness
>> of the mesh. Different mesh and different size of clips gives
>> different discrepancies, and I cannot find any obvious relationship
>> between the paraview-calculated volume and the real volume.
>
> When I create a 100^3 wavelet and clip it with a sphere of radius 20,
> I am getting a volume of 33447.5 which is pretty close to the analytic
> value of 33510.3. Can you send me a dataset that demonstrates this
> problem?
>
>> 2) X-Y plot: how can I do a xyplot of a scalar along a curved line?
>> For example, if I have the pressure field data from a
>> flow-around-a-cylinder case, I want to plot the pressure along the
>> surface of the cylinder as a function of angle or arc length.
>
> You can't, yet. I am working on that feature for the next release.
>
>> 3) tensor calculation: I have the pressure field and velocity field
>> calculated from a CFD tool (Transat in my case), how do I calculate
>> stress tensors at each point from P V field in paraview?
>
> Let me ask a question back : do you have any Python knowledge? We are
> working on making this really simple but currently the array
> calculator is too limited and cannot produce tensors. However, this is
> doable using the programmable filter.
>
> -berk
>
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